header file cleanup

see http://seclists.org/nmap-dev/2013/q4/168

Move some includes out of nmap.h: nmap.h gets included lots of places,
and unconditionally included math.h, ctype.h, errno.h, stdio.h,
sys/stat.h, fcntl.h, sys/types.h, and stdarg.h. This commit moves those
includes into the .cc files where they are necessary and out of nmap.h

Remove redundant include global_structures.h, included from nmap.h

Removed redundant code included from nmap.h

Removing #include nbase.h when nmap.h is included (redundant)

Remove duplicate #include lines

Add ifndef guards to a few .h files

osscan2.h

@@ -129,8 +129,6 @@
 #define OSSCAN2_H
 
 #include "nmap.h"
-#include "global_structures.h"
-#include "nbase.h"
 #include <vector>
 #include <list>
 #include "Target.h"